Electric shaft furnace



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ELECTRIC SHAFT FURNACE Filed March 2, 1955 4 Sheets-Sheet l w am J.

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ELECTRIC Si-IAFT FURNACE Filed March 2, 1955 4 Sheets-Sheet 3 jt zrneyJuly 17, 1956 w. BRUGGER ELECTRIC SHAFT FURNACE 4 Sheets-Sheet 4 FiledMarch 2, 1955 INVENTOR. Mil/helm Bragg?" BY 9 3 7 6 0 M W W 2 W 5 n06 ww x00 L G 1 MW w .2. %/y 5 .5 m

United States PatentO ELECTRIC SHAFT FURNACE Wilhelm llrugger, Essen,Germany, assignor to Th. Goldschmidt A. G., Essen, Germany, a Germancompany Application March 2, 1955, Serial No. 491,599 Claims priority,application Germany March 5, 1954- 14 Claims. (Cl. 1323) This inventionrelates to electric shaft furnace; and it comprises a shaft furnacewhich is particularly adapted to be used in the halogenation of oxidicores, metallic oxides and the like, comprising a metallic furnacejacket, an acid-resistant refractory lining inside said jacket, areplaceable cylindrical insert of an electrically-conducting,heat-resistant carbon material, selected from the class consisting ofamorphous carbon and graphite, mounted inside said lining, a screen ofsaid carbon material mounted horizontally inside said insert and servingto divide the interior into a lower melting zone and an upper reactionzone, a graphite electrode having a central bore mounted centrallyinside said insert, an electrically-conducting heat-resistant carbonmaterial making surface contact only with the lower end of saidelectrode for supporting the same above said screen and for conductingelectric current therefrom to said screen and said insert, means forcontrollin the pressure of the electrode against the elec trodesupporting means thereby to control the contact resistances between theelectrode and the insert, means for charging the reaction zone withoxidic material to be halogenated, means for passing a gaseous halogenthrough the bore of said electrode into the bottom of the furnace justabove said screen, means for tapping off molten halides collecting insaid melting zone, means for collecting gaseous products from the top ofsaid insert, and means for passin an electric current through saidelectrode, through said screen and through said insert; all as morefully hereinafter set forth and as claimed.

It has long been known that various metal oxides can be reacted withcarbon and chlorine at high temperatures to form anhydrous chlorides.Thus, for example, aluminum chloride can be produced from aluminumoxide, carbon and chlorine in accordance with the following equations:

In practice highly reactive oxides of aluminum and magnesium are mixedin the ground state with coal dust, pulverised charcoal and a binder,pressed into briquettes or other granular shapes, and then used asstarting materials for the direct chlorination with chlorine gas.

The practical performance of direct chlorination or halogenation ofoxidic materials however constitutes such a difficult problem withrespect to corrosion that hitherto only relatively pure and intenselyreactive oxides, such as alumina and magnesia, have been used asstarting materials for the production of anhydrous chlorides on anindustrial scale. Compounds such as silica, zirconium oxide, berylliumoxide, and various other oxidic ores, however, are far less reactive, sothat extremely high reaction temperatures are required for theirreaction with carbon and chlorine. This applies to compounds ofdifferent oxides with one another, for example to silicates such asorthite, cerite, zirconium sand, and so on, and also to ores having ahigh content of impurities, such as bastnaesite. In order ot obviatethese difliculties, for example in the known production of zirconiumtetrachloride from zirkon Patented July 17, 1956 sand, the zirkon sandis first reacted with carbon to form zirconium carbide and/or zirconiumcyanonitride and volatile silicon monoxide, and the zirconium carbide orzirconium cyanonitride is reacted with chlorine to form zirconiumtetrachloride only in a second stage. it has also already been proposed,for other difiicultly producible anhydrous chlorides, first to producethe sulphides and to convert these into the corresponding chlorides bydirect chlorination.

The particular ditficulties which occur in the direct chlorination orhalogenatio-n of difficultly reactive oxidic materials with carbon andchlorine or halogen on an industrial scale are caused by the highreaction temperatures required, namely about 1200 to 1500 C., since inthis temperature range the metal oxide components of refractory bricksof conventional industrial chlorination furnaces are themselvesconverted into anhydrous chlorides in the region of the reaction zone.Since quartz or porcelain bricks also constitute an oxidic material,these are also chlorinated under these conditions. Lining the innerfurnace shaft with carbon or graphite bricks also fails to providesatisfactory protection for the chlorinating furnace, since at the highreaction temperatures these materials are gradually oxidized by theoxidic starting material. Renewal of the inner brick layers ofchlorination furnaces or reactors is difficult or practicallyimpossible.

in the present invention i provide a furnace construction in which theabove described difficulties are substantially overcome. My furnace canbe operated successfully at extremely high temperatures. Corrosion isminimized and those parts which are subject to corrosion or erosion canbe readily replaced.

in my furnace I provide the conventional furnace jacket of iron or thelike and this is lined with a refractory, such as fire clay oracid-resistant brick, in the conventional manner. But inside therefractory lining I provide a replaceable cylindrical insert ofamorphous carbon or graphite which is spaced from the refractory lininga slight distance and which in effect forms an inert inner lining forthe furnace. This spacing, l have found, substantially increases thelife of both the refractory and the insert. Chlorine or other halogen isconducted into the bottom of the furnace through a central graphiteelectrode. A screen of graphite is mounted horizontally inside theinsert and serves to divide the interior into a lower melting zone forcollection of molten halides and an upper reaction zone in which thehalides are formed. A layer of granulated coke or other heat-resistantelectrically-conducting granular carbon material, such as graphite oramorphous carbon, is placed on top of the screen. This granular layerhas the function of dispersing and distributing the halogen before it ispassed through the furnace charge and in addition this layer passes atleast part of the electric current from the electrode to the insert.Numerous points of contact resistance are provided where the granules ofcoke touch each other and these resistances, being in the path of thecurrent, cause heating to be produced in the zone of this layer of coke.In one modification the central electrode rests on top of the coke layerand a spring suspension means is provided to suspend a controlledfraction of the weight of the electrode from above thereby altering thesum of the contact resistances and hence the temperature of the furnace.In another embodiment the graphite screen is supported on the shoulderof a graphite post while the central electrode rests loosely on top ofthe post which protrudes above the layer of coke. Here again the weightof the electrode resting on the post controls the sum of contactresistances in the path of the current passing from the electrode to thepost and then partly through the layer of coke but mostly through thescreen to the insert. Means are provided for collecting the gasesevolved from the furnace and for charging the furnace without permittingescape of the gases. Means are also provided for tapping off the moltenhalides which collect in the bottom of the furnace. The charge, whichconsists of shaped pieces of a mixture of oxidic material, such as ametal oxide ore, carbon and combustible binder in conventionalproportions, is charged on top of the layer of coke.

My invention can be explained in greater detail by reference to theaccompanying drawing which shows, more or less diagrammatically, anoperating embodiment of my shaft furnace. In this showing,

Fig. 1 is a front elevation of my furnace and superstructure with partbroken away in the furnace proper to show details of the electricallyconducting insert and screen,

Fig. 2 is an enlarged vertical section through a modified insert showinga removable screen and its support,

Fig. 3 is an enlarged partial vertical sectional view through thefurnace hood and upper part of the furnace, the partial section beingtaken between the lines 33 of Fig. 1,

Fig. 4 is a similar sectional view through the top of the centralelectrode of the furnace, extending between the lines 44 of Fig. 1,

Fig. 5 is a similar sectional view through the suspending means for thefurnace, taken between the lines 5-5 of Fig. 1,

Fig. 6 is a side view of the suspending means for the central electrode,

Fig. 7 is a partial vertical section on an enlarged scale showing theconstruction of the ceramic tubes in the central electrode which areused for conducting the chlorine gas into the furnace, taken along theline 7--7 of Fig. 4,

Fig. 8 is a horizontal section looking downwardly through the centralelectrode taken along the line 3-8 of Fig. 4,

Fig. 9 is a plan view of the top of the electrode taken along the line99 of Fig. 4,

Fig. 10 is a plan view of the furnace hood taken along the line 10-10 ofFig. 3, while Fig. 11 is a vertical sectional view looking downwardlytaken along the line 11-11 of Fig. 4.

In the various views like parts are designated by like referencenumerals. Referring first to Fig. l the main parts of my shaft furnacecomprise the furnace proper shown generally at 1, the hood showngenerally at 2, the electrical connection and cooling means for thecentral electrode 5, shown generally at 3, and the spring suspen sionmeans for the central electrode, shown generally at 4. As shown in Fig.1 the furnace has an iron jacket 6, a lining of refractory material 7,which may be acid resistant bricks, and is provided at its bottom 3 witha tapping means 9. Inside the refractory lining of the furnace anannular replaceable insert 10 is positioned which in effect forms acorrosion-resistant lining but it is spaced a slight distance from therefractory lining. The lower portion of the insert, which is the onlyportion subjected to the maximum temperature reached in the furnace, isconstructed of graphite and the space between the graphite insert andthe refractory ensures a long life for the latter. The entire insert canbe constructed either of graphite or amorphous carbon, if desired, orthe insert can be made in two or three interfitting parts, as shown inFig. 2 where the central portion 11 is constructed of amorphous carbonwhich has the advantage of having a lower thermal conductivity thangraphite thus causing the maximum heat to be concentrated in the lowerpart of the furnace. But it is advantageous to provide an upper contactring 12, Fig. 2, of graphite where the insert makes electrical contactwith the iron contact plate 13; see Fig. 3.

The graphite or carbon insert 16 of Fig. l is provided with an integralhorizontal plate or screen 14 having vertical holes 15 through which themolten chlorides or halides formed in the furnace pass to the bottom ofthe furnace from which point they can be tapped through the tappingmeans 9. On top of the screen 14 a layer 16 of granular heat-resistantconductive material, such as coke, is placed and the central electrodeof graphite 5 rests on the top of this coke layer. The electric currentpasses from the central electrode through the layer of coke, then to thescreen 14 to the graphite or carbon insert 10 and finally out throughthe top of the insert to the contact plate 13. This contact plate isprovided, as shown in Fig. 11 with 18 contact elements 39 symmetricallyarranged about its periphery. All or any of these can be connected to asource of electricity by means of contact plugs 17; see Figs. 1, 3 and11. The heating is produced by the contact resistance between thecentral electrode and the coke layer as well as between the individualgranules of coke. The graphite insert 19 is supported a slight distanceabove the furnace bottom 8 by means of graphite discs 13 so that theanhydrous molten halide which collects on the bottom of the furnace canreadily flow to the tapping hole.

In the modification shown in Fig. 2 the screen 14a is formed as aseparate part and has a sliding fit in the insert 10a and is supportedby means of a central post 19 of graphite which rests on the bottom a ofthe furnace. The upper part 20 of the post is reduced in diameter whereit passes through the screen leaving an annular shoulder 21 on which thescreen rests. In this embodiment the post has a head 22 having acone-shaped top surface which is provided with several grooves orrccesses 23 which form passageways for the chlorine or other halogenwhich is passed downwardly through the central bore 24- of the electrode5, through the recesses and then upwardly through the briquetted charge25 of ore or the like to be halogenated. The bottom surface of theelectrode conforms in shape to the shape of the top surface of the postwhere these surfaces engage. This ensures good electrical contact. itwill be seen that the furnace charge rests on top of the coke layer 16which in turn rests on top of the screen 1411. The top of the post risesslightly above the layer of coke so that the electrode 1t) rests on topof the post. in this embodiment the electric current passes from thecentral electrode to the head of the post and then partly through thelayer of coke but mostly through the post to the screen and/or to theinsert, heating being due to the contact resistances in the path of thecurrent.

Owing to the high heat conductivity of the graphite insert sufiicientheat is diverted both upwardly and downwardly from the layer of coke andthe screen so that the entire reaction chamber, that is, the meltingchamber below the screen and the reaction chamber above the screen, isheated adequately to cause the chemical reaction to take place and tokeep the molten halidc in the bottom of the furnace in fluid conditionso it can be readily tapped. As compared with graphite the heat conduotivity of amorphous carbon is low so that, in the modification of Fig. 2the upper part of the furnace remains cooler than in the modificationshown in Fig. 1. Heat losses are therefore smaller. if desired theseveral parts of the insert of Fig. 2 can be screwed or otherwisesecured together. Otherwise they may be supported loosely on each otheras indicated in the figure.

In order to protect the amorphous carbon portion 11 of the insert ofFig. 2 from corrosion by volatile chlorides, such as ferric chloride,aluminum chloride, zip.

conium chloride etc., this portion of the insert can he impregnated withan alkali metal silicate solution or with a concentrated solution ofphosphoric acid. This caution is not necessary with all-graphite insertsthe graphite conducts the heat upwardly sufiiciently so that thetemperature of the insert remains above the condensation temperatures ofthe gaseous halides.

The construction of the upper part of my furnace is shown best in Figs.3, l0 and 11. It will be seen from Figs. 3 and ll that the contact plate13 is annular but that on three sides bracket plates 26 are weldedthereto,

these forming in effect extensions of the contact plate.

Each of the bracket plates is provided with a vertical strengthening fin27 and mounting plates 28 are attached by bolts 29 to two of the bracketplates, the mounting plates in turn being mounted on a foundation, notshown, 5 which may be used to support the furnace. At the outer ends ofthe bracket plates tightening bolts 39 are provided. The lower ends ofthese bolts are pivoted at 31 to lugs 32 welded to the top of thefurnace jacket 6. When the bolts 3d are tightened this prc s the contactplate i3 against the top of the conducting insert to improve theelectrical contact between these elements. The contact plate can becooled by passing water through annular water jacket 3", introducing itthrough inlet tube 33 and discharging it through outlet tubes 34 (Fig.ll).

The space (Pig. 3) between the conducting insert it and the refractorylining 7 of the furnace is sealed off at the top by means of a layer 36of acid proof cement. Another layer 37 of a thermosetting resin, such asasplit or coumarone resin, can be introduced above the cement 20 layer,this resin layer being cooled by water passing through the lead tubing33, if desired. The conducting insert can be replaced easily whenrequired by removal of the cement and resin seals.

The furnace proper is surmounted by the hoodstructure shown generally at2. The hood structure is cement d tightly to the iron contact plate 13by means ll g of asbestos or acid proof cement. T he hood is providedwith a covered cleaning hole and with a exhaust fine A charging funnelas the top of the hood structure.

of which has a charging aperture clc ed and by the conventional chargingvalve mechanism &5 (P 3) operated by valve handles The oper structure ofthe charging valve mechanism are believed to be evident from the drawingwhich shows that openings 4'7 in top plate are opened to permit entryinto the funnel of the briquettes to be charged only when the chargingapertures 4d are closed. This pre .ts cs cape of gases during thecharging operation. The hood structure can be insulated from the centralelectrode by insulation shown at 49, if desired.

The electrical connections for the central electrode are shown best inFigs. 4- and The contact clamp dd is made in two parts which fit aroundthe electrode 5 and are clamped together with bolts 51. Vertical grooves52 are provided in the inside surface of the cl mp, where the centralbore of the electrode, as shown best 7. The outer tube 55' serves an impins list-- ing for the bore, While the halogen is passed through thecentral tube A stuffing box or packing gland g asbestos or other packing*eals oil the end of tube 1d prevents tl'e halogen from upwardly. Meansmust be provided to tighten the packing gland owing to the differentrates of thermal expansion of the various parts. For this purpose Iprovide at the top of the electrode 5 a threaded bore into which isscrewed a threaded nipple 5'8 which extends a short distance above thetop of the electrode. An iron plate 59 is screwed to the top of thenipple. Four screws 59 are threaded into the top of the iron plate.These screws pass through holes drilled in a second iron plate d1. Thisupper plate has a 75 central bore which i s just large enough for theinner ceramic tube 56 to pass therethrough. The plate therefore rests onthe upper end the outer ceramic tube 55, the plate being counterboredfrom below to receive the upper end of this tube. It is evident thatwhen the nuts 62 on screws 60 are tightened, this presses the outerceramic tube downwardly thereby compressing the packing in the gland 57.It will be noted from Fig. 7 that the central bore 24 of the electrodeis provided with shoulders 63 and 64. The inner ceramic tube 56 rests onshoulder 63 while the shoulder 64 supports packing gland 57.

The inner ceramic tube 56 passes upwardly through the iron plate 61 andextends for a short distance above this plate. A hose 65 of rubber orplastic is attached to the top of the tube and this hose suppliesgaseous halogen to the furnace.

The central electrode is advantageously supported by means forcontrolling the downward thrust of the electrode against the layer ofcoke 16 (Fig. l) or the post head 22 of Fig. 2. This downward thrustcontrols the contact resistance between the lower end of the electrodeand the conducting insert 16 and therefore the resistance of thefurnace. Such a controlling means is shown generally at 4 in Fig. 1 andin more detail in Figs. 5 and 6. As shown in these figures the bars Edaextend upwardly above the central electrode and at their upper ends theyare provided with a notch 66 which is adapted to receive a horizontalsuspending rod 67. This rod has a central vertical bore which receiveswith a sliding fit a sleeve or bushing 63 of insulating material. Athreaded rod 69 extends through the central bore of this sleeve andflanged nut 69a is threaded on the lower end of the rod while at itsupper end the rod terminates in a suspending loop 78 above a horizontalflange 71 which rests on the upper end of the insulating sleeve which atthis point has an integral flange 72 which rests on top of thesuspending rod. An insulating washer 73 is mounted on the insulatingsleeve directly below the suspending rod and a coil compression spring74 is mounted between the flanged nut 69a and the washer 73. It isevident that, when loop '76 is engaged with a fixed support, not shown,and when flanged nut 6% is a tightened, this tends to raise thesuspending rod 67 and therefore the vertical bars 5 5a and the centralelectrode 5. This would increase the resistance of the furnace. Thus thespring suspension which has been described can be used to control theresistance and hence the electric current passing through the furnace,i. e. to control the furnace temperature. This makes it possible to heatup my furnace rapidly even though the insert it? should consist of asingle tube of amorphous carbon.

The weight of the central electrode resting on the layer of coke (Fig.l) or on the head of the contact post (Fig. 2) was found sufficient toloa er the contact resistance in one furnace to the point where adequateheating was provided when the furnace was operated at from 19 to 25volts and at from about lOOO to 2500 amps. This ft nace has a graphiteinsert havin an outer diameter of 500 mm. and an inner diameter of 300mm. resting on three graphite discs serving as feet. The inner diameterof the furnace shaft (refractory) was 520 mm. The graphite screen had athickness of ll); lit) him. while the head of post of 2 ex 'ifid about159 mm. above the screen. The central electrode had a diameter of aboutmm. and a bore of about 15 mm. diameter. The screen of Fig. 2 may have adiameter of 295 mm.

In a furnace having the construction shown in Fig. 2 a controllablefraction of the current passes through the molten halides at the bottomof the furnace and hence these halides can be maintained readily inmolten condition. This construction has the further advantage that theamount and temperature of the melt can be judged to a certain extent bythe readings of the electrical instruments connected into the electricalcircuit since all of the electrical conductors inside the furnace have astrongly negative temperature coefiicient of resistance.

"When inserts comprising amorphous carbon are employed it is always anadvantage to provide an upper section of graphite where the insertcontacts the iron contact plate 13 in order to provide a betterelectrical contact with the plate. This graphite section may have alength of from 100 to 150 mm. for example. In the absence of such asection difiicult electrical contact conditions may develop at the pointof contact between the contact plate and the insert if the furnace isoperated on a high load.

The construction of the furnace hood may be varied in accordance withthe disposal to be made of the gases evolved. When fusible salts are tobe produced in the furnace the volatile halides, which may then beproduced in small amounts, may be without value and the gases evolvedcan then be merely collected, chemically decomposed and neutralized. Incase valuable fusible and volatile halides are produced simultaneously.however, a tightly fitting furnace hood is required so that the volatilehalides can be recovered from the furnace gases. Further treatment wouldfollow conventional practices.

A particular advantage of the hereindescribed shaft furnace is that itcan be operated at very high reaction temperatures. The upper limit forthe reaction temperature required is determined by the fact that theboiling points of most of the molten chlorides lie below 2000 C. Thethroughput through the aforedescribed chlorination furnace is high. Witha shaft diameter of 300 mm., about 50 kg. of zirconium sand or 50 kg. ofbastnaesite or 60 kg. of cerite oxides, in the form of coal-orebriquettes, can be reacted per hour to form the corresponding chloridesor halides. The upper limit of the furnace throughput is determined bythe gas speed, because if this limit were exceeded the briquettedstarting material would be blown out of the furnace.

Another advantage of my furnace construction is that no electrical leadsare passed through the ceramic lining of the furnace. My electricalconnections are made above the furnace proper where they can be readilyinspected and replaced if necessary. The connections for the gaseoushalogen are also above the furnace. Only a very small amount of electriccurrent passes through the briquetted charge on account of the lowfurnace voltage. In contrast the layer of coke and the graphite parts inthe bottom of the furnace are highly conducting. Intense heating istherefore produced where it is required and no arcing is produced evenat very high temperatures. This is extremely important since arcingcould produce intense local over-heating, volatilization losses etc.

While I have described what I consider to be the most advantageousmodifications of my furnace it is obvious, of course, that variousdetails of construction can be varied without departing from the purviewof the invention. Thus the carbon used in the briquettes of the chargecan be pulverized coal dust, carbon black, coke or charcoal. Theconstruction of the composite conducting insert of Fig. 2 can be variedconsiderably. Thus the separate parts may be threaded, as at '75, andscrewed together or they may merely rest loosely on top of each other,as shown at 76. Water cooling of the various furnace parts may beemployed where desired or required. And, of course, various means can beused to control the downward pressure of the central electrode againstits support, thereby controlling the contact resistance and indirectlythe temperature of the furnace. Other modifications of this inventionwhich fall within the scope of the following claims will be immediatelyevident to those skilled in this art.

What I claim is:

1. An electric shaft furnace adapted to be used in the halogenation ofoxidic ores, metallic oxides and the like, comprising in combination afurnace jacket, an acid-proof refractory lining inside said jacket, areplaceable cylindrical insert of an electrically-conducting,heat-resistant carbon material, selected from the class consisting ofamorphous carbon and graphite, mounted inside said lining, a screen ofsaid carbon material mounted horizontally inside said insert and servingto divide its interior into a lower melting chamber and an upperreaction zone, a graphite electrode mounted concentrically inside saidinsert, an electrically-conducting, heat-resistant electrodesupportingmeans making surface contact only with the lower end of said electrode,supporting the same above said screen and adapted to conduct electriccurrent from the electrode to the screen and to said insert, means forcontrolling the pressure of the electrode against theelectrode-supporting means thereby to control the contact resistances inthe path of the current from the electrode to the insert, means forcharging the reaction zone with oxidic material to be halogenated, meansfor passing a gaseous halogen into the reaction zone just above saidhorizontal screen, means for tapping 0d molten halides collecting insaid melting chamber, means for collecting gaseous products evolved fromthe furnace charge, and means for passing an electric current throughsaid electrode, through said screen and through said insert.

2. The furnace of claim 1 wherein the cylindrical insert is formed insections, the lowest section being of graphite while an upper section isof amorphous carbon.

3. The furnace of claim 2 wherein the top section of the insert is ofgraphite and wherein a metallic contact ring is in electrical contactwith the graphite section to conduct current therefrom.

4. The furnace of claim 1 wherein said screen of carbon material isintegral with the insert.

5. The furnace of claim 1 wherein said screen of carbon material is aseparate element fitting inside the insert and is supported on agraphite post resting on the bottom of the furnace.

6. The furnace of claim 5 wherein said graphite post extends above thescreen and the central electrode rests on top of the post, the postconstituting the supporting means for the electrode.

7. The furnace of claim 1 wherein the electrode is provided with acentral bore for conducting gaseous halogen into the reaction zone ofthe furnace.

8. The furnace of claim 7 wherein the central bore of the electrode islined with a ceramic tube above the furnace level and an electricalconductor is attached to the electrode at this point so that theconductor is protected from corrosion by gaseous halogen which in theabsence of the ceramic tube would diffuse through the wall of theelectrode.

9. The furnace of claim 1 wherein the electrode has a central bore forconducting gaseous halogen into the reaction zone and is supported on agraphite post which rests on the bottom of the furnace and extends ashort distance above the screen and wherein one of the contact surfacesbetween electrode and post is provided with re cesses to conduct thegaseous halogen from the bore into the charge in the furnace.

10. The furnace of claim 1 wherein said insert is unitary andconstructed of graphite.

11. The furnace of claim 1 wherein said insert is unitary andconstructed of amorphous carbon.

12. The furnace of claim 1 wherein said electrode supporting means is ashallow layer of granulated coke.

13. The furnace of claim 1 wherein said pressure controlling meanscomprises a spring support for the electrode and means for changing thetension on the spring.

14. An electric shaft furnace adapted to be used in the halogenation ofoxidic ores, metallic oxides and the like, which comprises incombination a furnace jacket, an acidproof refractory lining inside saidjacket, a replaceable insert of an electrically-conducting,heat-resistant carbon material, selected from the class consisting ofamorphous carbon and graphite, mounted inside and spaced a shortdistance from the refractory lining of the furnace, a screen of saidcarbon material mounted horizontally inside said insert and serving todivide its interior into a lower melting chamber and an upper reactionzone, a graphite electrode 9 having a central bore mounted inside saidinsert, an electrically-conducting, heat-resistant electrode-supportingmeans making surface contact only with the lower end of the electrode,supporting the same above said screen and adapted to conduct electriccurrent between the electrode and said insert, means for controlling thepressure of the electrode against the electrode-supporting means therebyto control the contact resistances in the path of the current betweenthe electrode and the insert, means for charging the reaction zone withbriquettes of carbon and oxidic material to be halogenated, means forpassing a gaseous halogen to and through the central bore of theelectrode to a point in the reaction chamber just above the screen,means for tapping oif molten halides collecting in said melting chamber,hood means for collecting 10 gaseous products evolved from the furnacemounted above with a gas-tight connection to said insert, and electricalcontact means mounted above the furnace for attaching a source ofelectricity to said electrode and to said insert.

References Cited in the file of this patent UNITED STATES PATENTS815,016 Heroult Mar. 13, 1906 1,463,970 Pope Aug. 7, 1923 1,562,684Brown Nov. 24, 1925 1,901,524 Moschel Mar. 14, 1933 2,447,809 MiguetAug. 24, 1948

1. AN ELECTRIC SHAFT FURNACE ADAPTED TO BE USED IN THE HALOGENATION OFOXIDIC ORES, METALLIC OXIDES AND THE LIKE, COMPRISING IN COMBINATION AFURNACE JACKET, AND ACID-PROOF REFRACTORY LINING INSIDE SAID JACKET, AREPLACEABLE CYLINDRICAL INSERT OF AN ELECTRICALLY-CONDUCTING,HEAT-RESISTANT CARBON MATERIAL, SELCTED FROM THE CLASS CONSISTING OFAMORPHOUS CARBON AND GRAPHITE, MOUNTED INSIDE SAID LINING, A SCREEN OFSAID CARBON MATERIAL MOUNTED HORIZONTALLY INSIDE SAID INSERT AND SERVINGTO DIVIDE ITS INTERIOR INTO A LOWER MELTING CHAMBER AND AN UPPERREACTION ZONE, A GRAPHITE ELECTRODE MOUNTED CONCENTRICALLY INSIDE SAIDINSERT, AN ELECTRICALLY-CONDUCTING, HEAT-RESISTANT ELECTRODESUPPORTINGMEANS MAKING SURFACE CONTACT ONLY WITH THE LOWER END OF SAID ELECTRODE,SUPPORTING THE SAME ABOVE SAID SCREEN AND ADAPTED TO CONDUCT ELECTRICCURRENT FROM THE ELECTRODE TO THE SCREEN AND TO SAID INSERT, MEANS FORCONTROLLING THE PRESSURE OF THE ELECTRODE AGAINST THEELECTRODE-SUPPORTING MEANS THEREBY TO CONTROL THE CONTACT RESISTANCES INTHE PATH OF THE CURRENT FROM THE ELECTRODE TO THE INSERT, MEANS FORCHARGING THE REACTION ZONE WITH OXIDIC MATERIAL TO BE HALOGENATED, MEANSFOR PASSING A GASEOUS HALOGEN INTO THE REACTION ZONE JUST ABOVE SAIDHORIZONTAL SCREEN, MEANS FOR TAPPING OFF MOLTEN HALIDES COLLECTING INSAID MELTING CHAMBER, MEANS FOR COLLECTING GASEOUS PRODUCTS EVOLVED FROMTHE FURNACE CHARGE, AND MEANS FOR PASSING AN ELECTRIC CURRENT THROUGHSAID ELECTRODE, THROUGH SAID SCREEN AND THROUGH SAID INSERT.